The present invention relates generally to solar energy receivers and more particularly to an improved point focus central solar energy receiver useful in producing heated air for application to power generation systems and industrial process heat systems.
Existing air heating point focus central solar energy receiver designs for producing air at about 514 degrees centigrade use an intermediate working fluid such as draw salt. The intermediate working fluid can be heated in either a cavity or an open central receiver. Above 514 degrees centigrade air is heated directly in a cavity-type receiver. Most designs involve moving air through a bank of tubes which is exposed to incident solar radiation. The radiation is absorbed on the tubes and transferred to the air. Variations on this approach use heat pipes or impingement heat transfer to improve performance. All of these approaches have several disadvantages. First, the reflection, reradiation, and convective losses from existing receiver designs are about 6 to 15%, depending on operating temperature, even though all of these designs are cavity receivers with associated added spillage losses and large size. Second, due to poor heat transfer between the air and the absorbing surface, a very large heat transfer area is required which, in turn, results in a large receiver.
One particular existing design uses a tower and cross-arm to mount a large bell-shaped ceramic matrix receiver which has solar radiation striking it only from the bottom. The tower must be a relatively tall one for this operation. There is an air inlet orifice on its covered side. Heated air is drawn from the top of the receiver. Combined reflection and reradiation losses are expected to be significant, especially at higher temperatures. In addition, the cavity design would have associated spillage energy losses.